1. Field of the Invention
This invention relates to a golf ball mold defining a spherical cavity free of a great circle which does not intersect with dimple-forming projections. It also relates to golf balls of the seamless type prepared using the mold.
2. Related Art
As is well known in the art, golf balls are generally molded using a mold comprising a pair of mold sections. The mold sections are removably mated to define a spherical cavity by their concave surfaces which are provided with a plurality of dimple-forming projections for indenting dimples in the surface of a golf ball being molded in the mold. A parting plane between the mold sections is located substantially at the equator of the cavity.
No dimple-forming projections are provided at the edge of the mold sections corresponding to the parting plane so that an endless land strip may be formed on the golf ball being molded. This is for convenience of manufacture because during molding, cover stock oozes out between the parting surfaces of the mold and cures thereat to form fins, and after removal from the mold, the molded ball must be polished for abrading off the fins.
However, the provision of an endless land strip along the parting plane interrupts the continuous arrangement of dimples, imposing a constraint on the dimple arrangement. The resulting non-uniform dimple arrangement is undesirable for the aerodynamic performance of the ball.
To overcome such inconvenience, a variety of molds for molding golf balls of the so-called seamless type have been proposed wherein dimple-forming projections are disposed across the parting surface. FIGS. 6, 7 and 8 illustrate such exemplary molds. These molds allow an increased freedom of arrangement of dimple-forming projections so that the dimple-forming projections may be distributed on the cavity surface in a more uniform and dense fashion.
More particularly, FIG. 6 is a plan view of the lower mold section near the parting surface as seen from the equator side of the cavity. FIG. 7 is an enlarged side view of the mold near the parting surface as viewed from the inside of the cavity. In this mold, dimple-forming projections 23 are disposed in the cavity surface so as to extend across the parting plane PL. One mold section (lower mold section 20b in FIG. 7) at the parting surface is provided with concave furrows 24 which are semi-circular in cross section and extend radially with respect to the cavity 22. In the furrows 24, shaping pins 25 each having a dimple-forming projection at a distal end are received. The pins 25 are secured to the parting surface by screws 26. The other mold section (upper mold section 20a in FIG. 7) at the parting surface is correspondingly provided with concave furrows 27 for receiving the shaping pins 25 fixedly secured to the lower mold section. It is noted that gates for injecting molding material therethrough are depicted at 28 in FIG. 6.
When a golf ball is molded in the mold shown in FIGS. 6 and 7, fins of the cover stock penetrating out along the parting plane of the mold are located along the periphery of dimples and on the same level as the land where access for abrasion is easy. That is, formation of fins within dimples or depressions where access for abrasion is difficult is avoided.
FIG. 8 is an enlarged side view of the lower mold section near the parting surface as viewed from the inside of the cavity. The parting surface of the mold section is corrugated to form corrugations 29. Dimple-forming projections 25 are disposed within each corrugation 29 and on a circumferential extension of the parting surface PL (or on the equator). Where the lower mold section is provided with corrugations 29, the upper mold section is provided with recesses for receiving the corrugations, though not shown. When a golf ball is molded in the mold shown in FIG. 8, fins of the squeezed-out cover stock are located along the periphery of the corrugations, avoiding formation of fins within dimples.
However, the mold of the type wherein shaping pins each having a projection at a distal end are secured by screws as shown in FIGS. 6 and 7 has the problem that on repeated use for a long period of time, the screws can be loosened to create gaps between the pins and the furrows. Once loosened, the pins can be shifted or disengaged, leaving a possibility that the disengaged pins are bit between the mold sections to damage or break the mold sections.
In the case of the mold of the type wherein the parting surface is corrugated as shown in FIG. 8, one mold section is manufactured by shaping with a hemispherical male model or master corresponding to the hemispherical shape of the desired golf ball. The range of angle of the master extending from the pole (north or south pole) of the cavity to the parting surface is increased by the amount of the corrugation and exceeds 90.degree.. The extended area of the master engages the mold section, prohibiting the mold section from being removed from the master.